I always wash fabrics when I bring them home from the store. I like knowing how the fabric is really going to look and feel when it's washed. (Also, a carryover from making clothes, and not wanting them to shrink so that they don't fit after spending all that time making them!)
However, I just put together my first quilt top from a jelly roll of batiks. I didn't want to try washing all these strips, so I assembled it without washing, and then washed the top before making the quilt sandwich. This seemed to work ok, with the only problem being that there was a lot of raveling that I had to clean up. It reminded me of working on a rag quilt!
I've never done a kit, so can't comment on that.
And, oh yeah, color catchers in the wash are a MUST!